Windows/Mac/Linux (Firefox): The RetailMeNot Firefox extension integrates your online shopping with coupon aggregation web site RetailMeNot to keep you abreast of deals and freebies available at the site you're currently visiting. Just surf to a shopping site and the RetailMeNot extension will automatically check for coupons and alert you of available deals for that site. We've highlighted the RetailMeNot web site before, including how we use it to save tonnes online, but we've never given the extension a go. It's been a little hit or miss in my tests (sometimes the offers aren't showing up when they should), but in all it could be a nice add-on for the online power shopper. The RetailMeNot extension is free, works wherever Firefox does.